Many truck fleets, such as those owned and operated by utility companies, include vehicles having a transmission-driven power take-off driving a hydraulic pump, the pump pressure being employed to drive some item of auxiliary equipment. The same applies to refuse trucks which may employ power take-off means to operate hydraulic pumps which, in turn, serve to power trash compactors carried by such trucks. That is, the auxiliary equipment may be in the nature of, for example, an earth auger which is employed to perform work and or in areas other than the vehicle itself or apparatus as a trash compactor which performs its work on the vehicle itself.
In any event, regardless of the nature of the auxiliary equipment, it and the related hydraulic pump may become damaged by overspeeding.
Since the auxiliary equipment is usually subjected to wide variations in load, the speed thereof will also vary, unless some means is provided for opening the throttle when the load increases and closing the throttle when the load decreases. Also, for most efficient operation of the auxiliary equipment, it is desirable to drive the power take-off, and thus the hydraulic pump, at a constant speed. From the standpoint of protection of the equipment, however, it is of great importance to prevent overspeeding when the load decreases.
In many cases the engine is already provided with a governor to limit its maximum speed. However, in most cases where the engine also drives such auxiliary equipment, the auxiliary equipment must be operated at some speed lower than the maximum speed of the engine, and probably even lower than the maximum governed speed of the engine.
The prior art, generally, has provided a combined engine and engine driven auxiliary equipment governor for an engine driven vehicle having a carburetor with a throttle valve therein where such governor comprised separate throttle actuating means for controlling the fuel flow past such throttle valve with a stop member for limiting the throttle opening by said actuating means for operating such equipment; the actuating means, operated by vacuum, is connected to conduit means leading to an air source for the continuous bleeding of air to the actuating means so long as governed engine or equipment speed has not been approached; a pair of centrifugal valves operatively connected to such conduit means were respectively driven in response to engine and equipment speed; such centrifugal valves were independently effective to progressively vary the degree of air bleed and therefore the magnitude of the vacuum applied to the throttle actuating means as the speed of the engine or the equipment approached governed speed. Such an arrangement was generally acceptable; however, because of governmentally imposed noise abatement regulations the vehicle engine speeds have had to be significantly reduced. This, coupled with the fact that less engine vacuum is available because of other added engine accessories relating to minimizing engine exhaust emissions, arising from regulations imposed by other governmental agencies, has resulted in a vacuum signal which is insufficient during part throttle engine operation for achieving proper governing characteristics.
Accordingly, the invention as herein disclosed and claimed is directed primarily to the solution of the preceding as well as other related and attendant problems.